JP4818286B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine that feedback-controls an actual air-fuel ratio so as to approach a target air-fuel ratio, and more particularly to a technique for suppressing air-fuel ratio overleaning during fast idle operation.

In Patent Document 1, when the oxygen sensor is inactive, the actual air-fuel ratio is controlled to match the target air-fuel ratio by open loop control, and when the oxygen sensor is activated, the actual air-fuel ratio is controlled by feedback control. It is described that control is performed so as to match the air-fuel ratio.
JP 2001-23479A

Conventionally, at the time of start-up, the fuel injection amount is greatly increased to form a rich air-fuel mixture, and then the increase amount is gradually decreased to make the air-fuel ratio lean, and the air-fuel ratio is returned to the target air-fuel ratio during idle operation Control is taking place.
By the way, deposits adhere to the injection hole of the fuel injection valve, so that the actual injection amount with respect to the injection time decreases, or the variation / deterioration of the air flow sensor and the water temperature sensor acts in the direction of calculating the fuel injection amount less, If a heavy fuel with a lower vaporization characteristic than the planned fuel is used, the air-fuel ratio becomes leaner than the intended air-fuel ratio.

When the air-fuel ratio tends to become lean as described above, if the amount of increase after start-up is reduced as usual, the air-fuel ratio may become much leaner than the original target air-fuel ratio. There is.
Here, when the air-fuel ratio sensor is activated and air-fuel ratio feedback control is started, correction is made so as to approach the original target air-fuel ratio.

However, due to the delay in response to feedback control, the lean tendency cannot be resolved quickly, and the air-fuel ratio becomes over lean.This reduces the torque generated by the engine and deteriorates operability, or misfires exceed the lean combustion limit. There was a possibility.
The present invention has been made in view of the above problems, and an object of the present invention is to provide an air-fuel ratio control apparatus for an internal combustion engine that can suppress overlean of the air-fuel ratio during fast idle operation.

Therefore, in the present invention, when the actual air-fuel ratio at the start of the air-fuel ratio feedback control is leaner than the second target air-fuel ratio that is richer than the first target air-fuel ratio required from the operating conditions at that time In addition, the actual air-fuel ratio is feedback-controlled toward the second target air-fuel ratio for a predetermined period from the start of the air-fuel ratio feedback control, and the actual air-fuel ratio is adjusted toward the first target air-fuel ratio after the predetermined period has elapsed. The fuel ratio was feedback controlled.

According to the above invention, if feedback control is performed based on the second target air-fuel ratio that is richer than the first target air-fuel ratio according to the operating conditions at that time, the actual air-fuel ratio is leaner than the first target air-fuel ratio. In this case, the deviation (air-fuel ratio error) between the actual air-fuel ratio and the target air-fuel ratio becomes larger.
As a result of correcting the actual air-fuel ratio with a large feedback correction amount based on this larger deviation, the lean error can be suppressed with better response.

  Therefore, even when deposits adhere to the nozzle holes of the fuel injection valve and the air-fuel ratio tends to become lean, feedback control based on the second target air-fuel ratio is started, so that the lean tendency Can be quickly eliminated to prevent over-leaning, and it is possible to prevent the deterioration of driving performance and the occurrence of misfire.

Embodiments of the present invention will be described below.
FIG. 1 is a system diagram of an internal combustion engine for a vehicle according to an embodiment.
In FIG. 1, an electronically controlled throttle valve 3 that controls the amount of intake air of the engine 1 is provided in an intake passage 2 of the internal combustion engine 1, and the intake air that has passed through the throttle valve 3 flows into the intake valve 4. Through the combustion chamber 5.

On the other hand, a fuel injection valve 6 is provided on the upstream side of the intake valve 4, and fuel injected from the fuel injection valve 6 is sucked into the combustion chamber 5 together with the intake air, and then into the combustion chamber 5. A mixture is formed.
The fuel injection valve 6 may be an in-cylinder direct injection internal combustion engine that directly injects fuel into the combustion chamber 5.

The fuel sucked into the combustion chamber 5 is ignited and burned by spark ignition by the spark plug 7. The gas after combustion in the combustion chamber 5 is discharged to the exhaust passage 9 through the exhaust valve 8 and purified by the exhaust purification catalyst 10 interposed in the exhaust passage 9.
Further, a canister 12 is provided for adsorbing and collecting fuel vapor generated in a fuel tank 11 into which fuel to be injected from the fuel injection valve 6 is placed. The canister 12 is disposed downstream of the throttle valve 3 by a purge passage 13. It is connected to the intake passage 2 on the side.

When the purge control valve 14 interposed in the purge passage 13 is opened and the suction negative pressure of the engine 1 is applied to the canister 12, the new introduced into the canister 12 through the fresh air introduction path 15. Along with the air, the fuel vapor desorbed from the canister 12 is supplied to the engine 1.
Fuel injection by the fuel injection valve 6, ignition by the spark plug 7, and opening / closing of the purge control valve 14 are controlled by an electronic control unit 20 incorporating a microcomputer.

The electronic control unit 20 receives signals from various sensors and switches, calculates the fuel injection control signal, ignition control signal, purge control signal, and the like by computing the input signal according to a program stored in advance. Output.
The various sensors and switches include an air flow sensor 21 that detects the intake air amount QA of the engine 1, a throttle opening sensor 22 that detects the opening TVO of the throttle valve 3, and a cooling water temperature (engine temperature) TW of the engine 1. A water temperature sensor 23 for detecting the crank angle sensor 24, a crank angle sensor 24 for outputting a reference crank angle signal REF for each reference angle position of the crankshaft 16 and a position signal POS for each unit angle, and an exhaust passage 9 upstream of the exhaust purification catalyst 10. A front air-fuel ratio sensor 25 that detects the air-fuel ratio AF based on the oxygen concentration in the exhaust gas, and is provided in the exhaust passage 9 on the downstream side of the exhaust purification catalyst 10, and the air-fuel ratio AF based on the oxygen concentration in the exhaust gas A rear air-fuel ratio sensor 26 for detecting the acceleration pedal, an accelerator opening sensor 27 for detecting an accelerator pedal depression amount ACC (not shown), An outside air temperature sensor 28 that detects the air temperature TA, a vehicle speed sensor 29 that detects a traveling speed (vehicle speed) VSP of the vehicle on which the engine 1 is mounted, an engine switch (ignition switch) 30 that is operated by the driver, and the like are provided. Yes.

The fuel injection amount by the fuel injection valve 6 is determined according to the water temperature or the like during startup (during cranking), and basically the intake air detected by the air flow sensor 21 after startup (after complete explosion). Based on the amount, it is determined so that an air-fuel mixture corresponding to the target air-fuel ratio at that time is formed.
The target air-fuel ratio is determined according to the water temperature at the time of cooling when the cooling water temperature is equal to or lower than a predetermined value, and after warming up when the cooling water temperature exceeds a predetermined value, the engine load / engine speed at that time It is decided according to.

Further, in the fuel injection control after starting, when the front air-fuel ratio sensor 25 is activated and the feedback stop condition (deceleration, fuel cut, etc.) is not satisfied, the front air-fuel ratio Based on the actual air-fuel ratio detected by the sensor 25, air-fuel ratio feedback control is performed.
The air-fuel ratio feedback control includes an air-fuel ratio feedback correction coefficient for correcting the fuel injection amount based on a deviation between the actual air-fuel ratio detected by the front air-fuel ratio sensor 25 and the target air-fuel ratio, for example, proportional / In this control, the actual air-fuel ratio is brought close to the target air-fuel ratio by calculating by integrating and differentiating operations.

The output of the rear air-fuel ratio sensor 26 is used for correcting the control point of the air-fuel ratio feedback based on the output of the front air-fuel ratio sensor 25, and the rear air-fuel ratio sensor 26 can be omitted. Further, the rear side can be an oxygen sensor that detects rich / lean with respect to the stoichiometric air-fuel ratio.
Next, the target air-fuel ratio setting process in the air-fuel ratio feedback control will be described in detail with reference to the flowcharts of FIGS.

The flowchart of FIG. 2 shows a main routine for setting the target air-fuel ratio, and this main routine is executed every predetermined minute time.
In step S100, when the air-fuel ratio feedback control is started, the actual air-fuel ratio detected by the front air-fuel ratio sensor 25 (hereinafter referred to as FB start actual A / F) is calculated (air-fuel ratio detecting means). . A / F represents an air-fuel ratio, and FB represents air-fuel ratio feedback control.

Details of the processing contents in step S100 are shown in the flowchart of FIG.
In the flowchart of FIG. 3, in step S111, it is determined whether or not the engine 1 has been started, in other words, whether or not the engine 1 is in a complete explosion state.
The determination after the start (complete explosion state) is determined after the start (complete explosion state) when the engine speed NE calculated based on the output of the crank angle sensor 24 exceeds a threshold value.

If it is determined that the engine has not started (completely exploded) (before or during startup), the process proceeds to step S113, and initialization is performed to set the actual A / F at the start of FB to zero. .
On the other hand, if it is determined that the engine has been started (complete explosion state), the process proceeds to step S112, where it is determined whether it is time to start air-fuel ratio feedback control.
As described above, the air-fuel ratio feedback control is started on the condition that the front air-fuel ratio sensor 25 is activated, and the activation of the front air-fuel ratio sensor 25 depends on the elapsed time from the end of cranking, the cooling water This is determined from the temperature, the output of the front air-fuel ratio sensor 25, the exhaust temperature, and the like.

When the air-fuel ratio feedback control is not started, that is, when the front air-fuel ratio sensor 25 is not activated and is in the open-loop control state of the air-fuel ratio, the routine proceeds to step S113 and the actual A / Initialize F to 0.
When the front air-fuel ratio sensor 25 is activated and the air-fuel ratio feedback control is started, the process proceeds to step S114, and the detection result (actual air-fuel ratio) of the front air-fuel ratio sensor 25 at the time when the air-fuel ratio feedback control is started. , Set to actual A / F at the start of FB.

When the FB start actual A / F is calculated as described above in step S100 of the main routine shown in the flowchart of FIG. 2, in the next step S200, a start time control end flag is set.
The details of the processing content in step S200 are shown in the flowchart of FIG.
In the flowchart of FIG. 4, in step S211, it is determined based on the output of the crank angle sensor 24 whether or not the engine 1 is rotating.

If the engine 1 is not rotating, that is, before the engine 1 is started, the process proceeds to step S212, and the start-time control end flag is cleared (reset to 0).
On the other hand, if it is determined that the engine 1 is rotating, the process proceeds to step S213, and it is determined whether or not it is the start time of the air-fuel ratio feedback control as in step S112.
If it is before the start of the air-fuel ratio feedback control, the process proceeds to step S214, the start-time control end flag is held at 0, and if the start of the air-fuel ratio feedback control is determined, the process proceeds to step S215, where the start-time control is performed. Set 1 to the end flag.

Therefore, the start-time control end flag is kept at 0 from the start of the engine 1 until the air-fuel ratio feedback control is started, and is switched to 1 with the start of the air-fuel ratio feedback control.
When the start-time control end flag is set as described above in step S200 of the main routine shown in the flowchart of FIG. 2, in the next step S300, the timer is updated after the start-time control ends.

Details of the processing contents in step S300 are shown in the flowchart of FIG.
In the flowchart of FIG. 5, in step S311, it is determined whether or not 1 is set in the start-time control end flag.
If the start-time control end flag = 0 and the air-fuel ratio feedback control is not started, the process proceeds to step S312, and initialization is performed to reset the timer to 0 after the start-time control ends.

On the other hand, if the start-time control end flag = 1 and the air-fuel ratio feedback control is started, the process proceeds to step S313, the timer is updated (counted up) after the start-time control ends, and the air-fuel ratio feedback is started. The elapsed time from the start of control is measured by a timer after the start-up control is completed.
In step S300 of the main routine shown in the flowchart of FIG. 2, when the timer is updated after completion of the start-time control as described above, a normal-time control switching end flag is set in the next step S400.

Details of the processing contents in step S400 are shown in the flowchart of FIG.
In the flowchart of FIG. 6, in step S411, it is determined based on the output of the crank angle sensor 24 whether or not the engine 1 is rotating.
When the engine 1 is not rotating, that is, before the engine 1 is started, the process proceeds to step S412 to clear the normal time control switching end flag (reset to 0).

On the other hand, if it is determined that the engine 1 is rotating, the process proceeds to step S413, where it is determined whether the start time control end flag is set to 1 and the air-fuel ratio feedback control is started.
If the start-time control end flag = 0 and the air-fuel ratio feedback control is not started, the process proceeds to step S416, and the normal-time control switching end flag is held at 0.

On the other hand, if the start-time control end flag = 1 and the air-fuel ratio feedback control is started, the process proceeds to step S414, where the air-fuel ratio feedback control measured by the timer after the start-time control ends is started. It is determined whether or not the elapsed time t has reached the delay time T.
The delay time T is set based on the actual A / F at the start of the FB.

Specifically, the actual A / F at the start of the FB is richer than the target air-fuel ratio (second target air-fuel ratio) corresponding to the coolant temperature at the start (the target air-fuel ratio at the start-up water temperature ≧ the actual at the start of the FB) A / F), the delay time T is set to 0 sec.
On the other hand, the actual A / F at the start of FB is leaner than the target air-fuel ratio (second target air-fuel ratio) corresponding to the cooling water temperature at the start (the target air-fuel ratio at the start-up water temperature <the actual A / F at the start of FB) ), The delay time T is set to 100 seconds, for example.

The delay time T under the lean condition is not limited to a constant value, and the larger the deviation between the target air-fuel ratio (second target air-fuel ratio) corresponding to the coolant temperature at start-up and the actual A / F at the time of starting FB is larger. The delay time T can be set longer as the actual A / F at the start of FB is leaner.
Until the elapsed time t reaches the delay time T, the process proceeds to step S416, and the normal control switching end flag is held at 0.

On the other hand, when the elapsed time t reaches the delay time T, the process proceeds from step S414 to step S415, where the target air-fuel ratio used in the air-fuel ratio feedback control at that time is the normal target air-space required from the operating conditions at that time. It is determined whether or not the fuel ratio (first target air-fuel ratio) matches.
If the target air-fuel ratio at that time does not match the normal target air-fuel ratio (first target air-fuel ratio), the process proceeds to step S416, the normal-time control switching end flag is held at 0, and the target air-fuel ratio is set. When the fuel ratio is equal to the normal target air-fuel ratio (first target air-fuel ratio), the process proceeds to step S417 and 1 is set to the normal-time control switching end flag.

That is, after the delay time T has elapsed since the start of the air-fuel ratio feedback control and the target air-fuel ratio at that time coincides with the normal target air-fuel ratio (first target air-fuel ratio), The control switching end flag is set to 1.
Therefore, when 1 is set in the normal-time control switching end flag, the air-fuel ratio feedback control based on the normal target air-fuel ratio (first target air-fuel ratio) required from the operating condition at that time is started. Indicates that

When the normal control switching end flag is set as described above in step S400 of the main routine shown in the flowchart of FIG. 2, the target air-fuel ratio mode setting process is performed in the next step S500.
Details of the processing in step S500 are shown in the flowcharts of FIGS.

In step S511, air-fuel ratio feedback control (normal control) based on the normal target air-fuel ratio (first target air-fuel ratio) required from the operating condition at that time is started by determining the normal-time control switching end flag. It is determined whether or not.
When the normal control switching end flag = 0 and the normal control is not started, the process proceeds to step S512, and it is determined whether the air-fuel ratio feedback control is started by determining the start time control end flag. .

If the start-time control end flag = 0 and the air-fuel ratio feedback control is not started, the process proceeds to step S514 to set the target air-fuel ratio mode to the 0th mode.
On the other hand, when the normal control is not started but the air-fuel ratio feedback control is started with the start time control end flag = 1, the process proceeds from step S512 to step S513, and the air-fuel ratio feedback control is started after the air-fuel ratio feedback control is started. It is determined whether or not the delay time T has elapsed.

Then, even if the air-fuel ratio feedback control is started, the process proceeds to step S514 until the delay time T elapses, the target air-fuel ratio mode is set to the 0th mode, and when the delay time T elapses, step S515 is performed. And the target air-fuel ratio mode is set to the first mode.
Therefore, during the period from the start of the engine 1 until the air-fuel ratio feedback control is started and until the delay time T elapses after the air-fuel ratio feedback control is started, the 0th target air-fuel ratio mode is set. A mode is selected.

In the 0th mode, before starting the feedback control, the feedforward control is executed so that the target air-fuel ratio a is reached, and then the feedback control is executed so that the target air-fuel ratio a is reached at the start timing of the feedback control. .
Then, after the delay time T has elapsed and until the normal control is started (after the delay time T has elapsed, the target air-fuel ratio becomes equal to the normal target air-fuel ratio), The first mode is selected as the fuel ratio mode (see FIG. 10).

However, as described above, the actual A / F at the start of FB is richer than the target air-fuel ratio corresponding to the cooling water temperature at the start (target air-fuel ratio at the start-up water temperature ≧ actual A / F at the start of FB). If so, the delay time T is set to 0 sec, and the normal target air-fuel ratio is used together with the start of the air-fuel ratio feedback control, as will be described later.
Therefore, if the actual A / F at the start of FB is richer than the target air-fuel ratio corresponding to the cooling water temperature at the start, the target air-fuel ratio mode starts the air-fuel ratio feedback control as shown in FIG. The mode is switched from the previous 0th mode to the normal control mode without going through the first mode (third control means).

If it is determined in step S511 that normal control is started with the normal-time control switching end flag = 1, the process proceeds to step S516, and it is determined whether the exhaust purification catalyst 10 is activated.
The determination of the activity of the exhaust purification catalyst 10 can be made from the elapsed time from the start (complete explosion), the cooling water temperature, the outputs of the front air-fuel ratio sensor 25 and the rear air-fuel ratio sensor 26, and the like. Alternatively, the active state can also be determined by detecting the exhaust temperature at the outlet or the temperature of the carrier of the exhaust purification catalyst 10 with a sensor.

When the exhaust purification catalyst 10 is activated, the process proceeds to step S517, and the target air-fuel ratio mode is set to the fifth mode.
On the other hand, when the exhaust purification catalyst 10 is not activated, the process proceeds to step S518, and it is determined whether or not the engine 1 is in an idle operation state.
If it is not in the idling operation state, the process proceeds to step S519 to set the target air-fuel ratio mode to the fourth mode.

If the vehicle is in an idling state, the process proceeds to step S520 to determine whether the vehicle speed is lower than the threshold value.
When the vehicle speed is equal to or higher than the threshold value, the process proceeds to step S519, and the target air-fuel ratio mode is set to the fourth mode, as in the case where the vehicle is not in the idle operation state.
On the other hand, when the catalyst 10 is in an inactive state and is in an idle operation state and the vehicle speed is lower than the threshold value, the process proceeds to step S521, and the automatic transmission combined with the internal combustion engine 1 is set to the neutral range (N range). Determine whether it is selected.

If it is not the neutral range (when the travel range is selected), the process proceeds to step S522, and the target air-fuel ratio mode is set to the third mode.
On the other hand, if it is in the neutral range, the process proceeds to step S523 to set the target air-fuel ratio mode to the second mode.
The neutral range includes a non-driving range such as a P range in addition to the N range.

The target air-fuel ratio mode will be schematically described. The 0th mode is a start state, the first mode is a transition period from start to fast idle, the second mode is a fast idle state, and the third mode is a travel range for starting. Is selected, the fourth mode corresponds to the start and travel state immediately after the first idle, and the fifth mode corresponds to the travel state after the catalyst is activated.
When the target air-fuel ratio mode setting process is performed as described above in step S500 of the main routine shown in the flowchart of FIG. 2, the target air-fuel ratio calculation process is performed in the next step S600.

Details of the processing content in step S600 are shown in the flowchart of FIG.
In step S611, it is determined whether or not the target air-fuel ratio mode at that time is the 0th mode.
If the target air-fuel ratio mode = the 0th mode, the process proceeds to step S612, and the target air-fuel ratio a calculated based on the coolant temperature at the start is set as the target air-fuel ratio at that time.

The target air-fuel ratio a is richer than the stoichiometric air-fuel ratio, and is set to be richer as the cooling water temperature at the time of starting is lower, thereby ensuring improved startability and rotational stability of the engine immediately after starting. .
The target air-fuel ratio a can be obtained by referring to a table in which the target air-fuel ratio a is stored in advance according to the cooling water temperature, and can be calculated from a function using the cooling water temperature at the start as a variable. it can.

If the target air-fuel ratio mode is not the 0th mode, the process proceeds to step S613 to determine whether or not the target air-fuel ratio mode at that time is the first mode.
If the target air-fuel ratio mode is the first mode, the process proceeds to step S614, where the target calculated from the target air-fuel ratio a based on the starting water temperature in the zeroth mode based on the cooling water temperature (operating conditions) at that time. The target air-fuel ratio b that changes to the air-fuel ratio c (normal target air-fuel ratio) is set as the target air-fuel ratio at that time.

Here, if the actual A / F at the start of FB is richer than the target air-fuel ratio a (second target air-fuel ratio) based on the starting water temperature, the cooling water at that time is calculated from the target air-fuel ratio a based on the starting water temperature. Stepwise change to the target air-fuel ratio c calculated based on the temperature (third control means).
As a result, in step S415 of the flowchart of FIG. 6, it is determined that the target air-fuel ratio is equal to the normal target air-fuel ratio, and 1 is set to the normal-time control switching end flag, whereby in the flowchart of FIG. As the target air-fuel ratio mode, one of the second to fifth modes for setting the normal target air-fuel ratio is selected.

If it is at the time of general start, it will shift to driving | running | working via a first idle (2nd mode) from start.
Therefore, when the actual A / F at the start of FB is richer than the target air-fuel ratio a (second target air-fuel ratio) based on the starting water temperature, the air-fuel ratio feedback control starts from the start as shown in FIG. Until this is done, the target air-fuel ratio a (second target air-fuel ratio) corresponding to the cooling water temperature at the start is set in the 0th mode.

When the air-fuel ratio feedback control is started, the air-fuel ratio feedback control is performed according to the target air-fuel ratio c (first target air-fuel ratio) calculated based on the cooling water temperature at that time (third control). means).
On the other hand, when the actual A / F at the start of FB is leaner than the target air-fuel ratio a (second target air-fuel ratio) based on the starting water temperature, the target based on the starting water temperature in the zeroth mode in the first mode. From the air-fuel ratio (second target air-fuel ratio) to the target air-fuel ratio c (first target air-fuel ratio) calculated based on the coolant temperature (operating conditions) at that time, gradually at a slower speed than in the case of rich. The air / fuel ratio at that time is used as the target air / fuel ratio b.

The target air-fuel ratio b has an initial value as the target air-fuel ratio a, and is then updated by incrementing a predetermined value Δb (b = b ₋₁ + Δb), and the update is stopped when the target air-fuel ratio c is reached. The leaning speed can be changed by setting the predetermined value Δb to a fixed value or a value set according to the water temperature.
When the actual A / F at the start of FB is leaner than the target air-fuel ratio a (second target air-fuel ratio) based on the water temperature at start-up, the 0th mode is continued for the delay time T even after the start of the air-fuel ratio feedback control (the first mode). 1 control means).

  Further, after the delay time T has elapsed, the target air-fuel ratio used for air-fuel ratio feedback control is gradually changed to the target air-fuel ratio c calculated based on the cooling water temperature at that time, and the cooling water at that time When the target air-fuel ratio c (first target air-fuel ratio) calculated based on the temperature is reached, air-fuel ratio feedback control with the normal target air-fuel ratio c (first target air-fuel ratio) is thereafter performed (second control). means).

Here, since the coolant temperature rises from the start and the target air-fuel ratio changes leaner as the coolant temperature rises, the target air-fuel ratio a (second target air-fuel ratio) based on the start-up water temperature is The target air-fuel ratio c is richer than the target air-fuel ratio c calculated based on the cooling water temperature after the start of air-fuel ratio feedback. In the first mode, the target air-fuel ratio is gradually made lean.
As described above, when the actual A / F at the start of FB is leaner than the target air-fuel ratio a (second target air-fuel ratio) based on the starting water temperature, a predetermined period from the start of the air-fuel ratio feedback control is Air-fuel ratio feedback control is performed based on the target air-fuel ratio that is richer than the target air-fuel ratio c (first target air-fuel ratio) required from the operating conditions (water temperature).

The speed (leanization speed) for changing from the target air-fuel ratio a corresponding to the cooling water temperature at the start to the target air-fuel ratio c calculated based on the cooling water temperature at that time is a fixed value. Alternatively, the slower the actual A / F at the start of FB, the lower the target air-fuel ratio a (second target air-fuel ratio) based on the water temperature at start-up, the slower the speed can be made.
For example, when deposits are attached to the injection holes of the fuel injection valve, the actual injection amount with respect to the injection time has decreased, or there is variation or deterioration in the direction of leaning the actual air-fuel ratio. In addition, if the increase in the fuel injection amount is reduced stepwise before the start of the air-fuel ratio feedback control after starting, the air-fuel ratio becomes leaner than when there is no deposit or the like.

  Here, when the air-fuel ratio sensor 25 is activated and the air-fuel ratio feedback control is started based on the normal target air-fuel ratio, the difference between the actual air-fuel ratio and the target air-fuel ratio is relatively small. There is a possibility that the lean tendency cannot be suppressed with good response, and the actual air-fuel ratio becomes over lean with respect to the target air-fuel ratio (first target air-fuel ratio) required according to the coolant temperature at that time There is.

In setting the target air-fuel ratio based on the cooling water temperature, in order to ensure combustion stability, a richer air-fuel ratio is set as a target when the temperature is lower. The target air-fuel ratio based is richer than the target air-fuel ratio based on the coolant temperature at the start of the air-fuel ratio feedback control.
Accordingly, when the actual A / F at the start of FB is leaner than the target air-fuel ratio a based on the starting water temperature, the target air-fuel ratio a based on the starting water temperature a (second If the target air-fuel ratio is used, feedback control can be performed with the target air-fuel ratio a (second target air-fuel ratio) that is richer than the normal target air-fuel ratio c (first target air-fuel ratio) as a target. .

Then, as a result of performing feedback control so as to approach the richer target air-fuel ratio, the air-fuel ratio is made richer than when feedback control is performed based on the normal target air-fuel ratio (first target air-fuel ratio). Since the correction amount is set larger, the lean tendency of the air-fuel ratio can be suppressed with good response, and the occurrence of overlean can be prevented (see FIG. 10).
In addition, the purpose of performing the air-fuel ratio feedback control at the target air-fuel ratio a based on the water temperature at start-up is to suppress the lean tendency before starting the feedback, so after the lean tendency can be sufficiently suppressed, The target air-fuel ratio is returned to the normal target air-fuel ratio (first target air-fuel ratio) to prevent the air-fuel ratio from being excessively rich by air-fuel ratio feedback control.

Therefore, the speed for changing from the target air-fuel ratio a to the normal target air-fuel ratio c based on the delay time T and the starting water temperature (first mode time) is a time sufficient to suppress the lean tendency. It is set appropriately so as to be secured.
Step S615 and subsequent steps in the flowchart of FIG. 9 show the setting of the normal target air-fuel ratio (first target air-fuel ratio) required according to the operating conditions at that time. In step S615, the target air-fuel ratio mode is the second mode. If the second mode is selected, the process proceeds to step S616, and the target air-fuel ratio c is calculated based on the coolant temperature at that time.

The target air-fuel ratio c is leaner than the stoichiometric air-fuel ratio, and is set to be richer as the cooling water temperature is lower. The target air-fuel ratio c is obtained by referring to a table that stores the target air-fuel ratio a in advance according to the cooling water temperature. In addition, it can be calculated from a function having the cooling water temperature as a variable. The target air-fuel ratio c can reduce HC (hydrocarbon) emission before catalyst activation.
The lean setting of the target air-fuel ratio c is preferably set to such an extent that NOx emission is not affected.

In step S617, it is determined whether the target air-fuel ratio mode is the third mode. If the third mode is selected, the process proceeds to step S618, and the target air-fuel ratio is based on the cooling water temperature at that time. d is calculated.
Here, in both the second mode and the third mode, the target air-fuel ratios c and d are calculated according to the cooling water temperature at that time. In the second mode, the target air-fuel ratio c suitable for idle operation in the neutral range is calculated. In the third mode, the target air-fuel ratio d suitable for idle operation in a state shifted from the neutral range (N range) to the travel range (D range) is set.

The neutral range includes a non-driving range such as a P range in addition to the N range.
In step S619, it is determined whether or not the target air-fuel ratio mode is the fourth mode. If the fourth mode is selected, the process proceeds to step S620, where the target air-fuel ratio mode is determined from the engine speed and the engine load at that time. The fuel ratio e is calculated.

The target air-fuel ratio e can be obtained by referring to a map in which the target air-fuel ratio e is stored in advance according to the engine speed and the engine load, and is calculated from a function using the engine speed and the engine load as variables. can do.
Since the target air-fuel ratios d and e are in the travel mode, the catalyst is not activated by setting the target air-fuel ratio near the stoichiometric air-fuel ratio on the rich side compared to the target air-fuel ratio c in order to ensure engine torque. HC reduction and drivability improvement can be ensured.

Further, in step S621, it is determined whether or not the target air-fuel ratio mode is the fifth mode. If the fifth mode is selected, the process proceeds to step S622, where the engine speed and the engine load at that time are used. A target air-fuel ratio f is calculated.
The target air-fuel ratio f is set according to the oxygen storage amount of the catalyst, and about half of the oxygen storage amount of the catalyst is set as the target oxygen storage amount, while the actual oxygen storage amount is calculated and the target oxygen storage is calculated. The target air-fuel ratio f may be set so as to be an amount.

In the fourth mode and the fifth mode, the target air-fuel ratios e and f are calculated from the engine speed and the engine load at that time, but the same depending on whether or not the exhaust purification catalyst 10 is activated. Different target air-fuel ratios are calculated even under operating conditions.
By the way, as the second target air-fuel ratio that is richer than the first target air-fuel ratio required from the operating conditions (water temperature, engine speed, engine load, etc.) at the start of the air-fuel ratio feedback control, In addition to the target air-fuel ratio corresponding to the air-fuel ratio, an air-fuel ratio that is richer by a predetermined value than the first target air-fuel ratio can be set as the second target air-fuel ratio.

Further, the predetermined value can be variably set based on the difference between the first target air-fuel ratio and the actual A / F at the start of FB, and / or the leaning speed of the actual air-fuel ratio before starting the feedback.
Further, the change time of the target air-fuel ratio in the delay time T and / or the first mode is determined by the difference between the first target air-fuel ratio and the actual A / F at the start of FB and / or the actual air-fuel ratio before the start of feedback. It can be variably set based on the leaning speed.

Further, the delay time T and / or the target air-fuel ratio change rate in the first mode can be learned based on the air-fuel ratio change immediately after the start of air-fuel ratio feedback at the time of first idling.
Specifically, when the air-fuel ratio immediately after the start of air-fuel ratio feedback at the time of the first idle becomes leaner than a target air-fuel ratio required from the operating conditions at that time, the delay at the time of the next first idle A period in which the air-fuel ratio feedback control is performed based on a target that is richer than the normal target air-fuel ratio by making the time T longer and / or making the change rate of the target air-fuel ratio in the first mode slower. Is made longer and the second target air-fuel ratio is changed to be richer, so that leaning immediately after the start of feedback control is suppressed.

Further, the lean tendency of the air-fuel ratio can be determined from the air-fuel ratio learning correction value, and the delay time T, the change rate of the target air-fuel ratio in the first mode, the second target air-fuel ratio, and the like can be learned.
In the above embodiment, when the actual A / F at the start of FB is richer than the second target air-fuel ratio, it is immediately changed to the first target air-fuel ratio, but in a shorter period of time than when it is lean, An inclination may be set.

  In particular, when the target air-fuel ratio is changed stepwise as in the embodiment, a sudden change in torque occurs. Therefore, by setting a slope so as to suppress this, the target air-fuel ratio is prevented while preventing a sudden change in torque. Can be changed.

1 is a system diagram of an internal combustion engine in an embodiment of the present invention. The flowchart which shows the main routine of the calculation process of the target air fuel ratio in embodiment of this invention. The flowchart which shows the calculation process of the real air fuel ratio at the time of the air fuel ratio feedback control start in embodiment of this invention. The flowchart which shows the setting process of the starting control end flag in embodiment of this invention. The flowchart which shows the update process of the timer after completion | finish of control at the time of start in embodiment of this invention. The flowchart which shows the setting process of the normal time control switching end flag in embodiment of this invention. The flowchart which shows the setting process of the target air fuel ratio mode in embodiment of this invention. The flowchart which shows the setting process of the target air fuel ratio mode in embodiment of this invention. The flowchart which shows the calculation process of the target air fuel ratio in embodiment of this invention. The time chart which shows the characteristic of the target air fuel ratio when the air fuel ratio in the embodiment of the present invention has a lean tendency. The time chart which shows the characteristic of the target air fuel ratio when the air fuel ratio in the embodiment of the invention of this application is not lean.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Intake passage, 3 ... Throttle valve, 4 ... Intake valve, 5 ... Combustion chamber, 6 ... Fuel injection valve, 7 ... Spark plug, 8 ... Exhaust valve, 9 ... Exhaust passage, 10 ... Exhaust purification Catalyst, 16 ... crankshaft, 20 ... electronic control unit, 21 ... air flow sensor, 22 ... throttle opening sensor, 23 ... water temperature sensor, 24 ... crank angle sensor, 25 ... front air / fuel ratio sensor, 26 ... rear air / fuel ratio sensor, 27 ... accelerator opening sensor, 29 ... vehicle speed sensor

Claims (8)

In an air-fuel ratio control apparatus for an internal combustion engine that inputs an air-fuel ratio signal indicating an actual air-fuel ratio of the internal combustion engine, calculates and outputs an air-fuel ratio feedback control signal based on the actual air-fuel ratio and the target air-fuel ratio,
Air-fuel ratio detection means for detecting an actual air-fuel ratio at the start of the air-fuel ratio feedback control after engine startup;
When the actual air-fuel ratio at the start of the air-fuel ratio feedback control is leaner than the second target air-fuel ratio set to be richer than the first target air-fuel ratio required from the operating conditions at that time, First control means for performing feedback control of an actual air-fuel ratio toward the second target air-fuel ratio for a predetermined period from the start of the air-fuel ratio feedback control;
Second control means for performing feedback control of an actual air-fuel ratio toward the first target air-fuel ratio after the predetermined period has elapsed;
An air-fuel ratio control apparatus for an internal combustion engine, comprising:   When the actual air-fuel ratio at the start of the air-fuel ratio feedback control is richer than the second target air-fuel ratio, the first control unit sets the predetermined period to be shorter than when it is lean. 2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein an actual air-fuel ratio is feedback-controlled toward the second target air-fuel ratio.   When the actual air-fuel ratio at the start of the air-fuel ratio feedback control is richer than the second target air-fuel ratio, the actual air-fuel ratio feedback control is started from the start of the air-fuel ratio feedback control toward the first target air-fuel ratio. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, further comprising third control means for feedback-controlling the air-fuel ratio.   When the actual air-fuel ratio at the start of the air-fuel ratio feedback control is leaner than the second target air-fuel ratio, the first control means lengthens the predetermined period as the degree of leaning increases. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1.   In the case where the actual air-fuel ratio at the start of the air-fuel ratio feedback control is leaner than the second target air-fuel ratio, the first control means increases the degree of leaning and increases the second target air-fuel ratio. 2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein a period for holding the engine is set long.   In the case where the actual air-fuel ratio at the start of the air-fuel ratio feedback control is leaner than the second target air-fuel ratio, the second control means increases the degree of leaning and increases the second target air-fuel ratio. 6. The air-fuel ratio control apparatus for an internal combustion engine according to claim 4, wherein the change speed from the first to the first target air-fuel ratio is reduced. The predetermined period is made up of a retention time for the second target air-fuel ratio, a transition period from the second target air-fuel ratio to a first target air-fuel ratio,
When the actual air-fuel ratio at the start of the air-fuel ratio feedback control is richer than the second target air-fuel ratio, the first control means shortens at least the holding period as compared with the case where it is lean. The air-fuel ratio control apparatus for an internal combustion engine according to claim 2, characterized in that:   The air-fuel ratio control apparatus for an internal combustion engine according to any one of claims 1 to 7, wherein the first control means sets the second target air-fuel ratio based on an engine temperature at the time of starting.

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